The overall objective of the project was to provide guidance for selecting cost-effective interim management methods to control overtopping of impoundments, pits, ponds, or lagoons at uncontrolled hazardous waste sites until final remedial actions could be initiated. Hazardous waste impoundments are subject to overtopping through the collection of rainwater, run-on, or other uncontrolled inflow. Lagoon overflows are generally the result of insufficient capacity due to either insufficient freeboard (high level of lagoon contents) or structural problems that reduce the effective capacity. No matter what the cause, lagoon overflows can pose significant environmental and public health risks through the contamination of soils, groundwater, and surface water, as well as the potential to spread the contamination into areas not currently impacted by the lagoon. Thus interim measures may be necessary to control lagoon overflows prior to identification and selection of a final remedial measure. A manual has been prepared that addresses both immediate control measures for emergencies and longer term measures lasting several months to several years. The technology and cost guidance presented is general in nature because of the variability of waste lagoons and impoundments and the unique conditions and considerations that exist at each site. Where possible, factors affecting application, technology selection, and costs are identified, as well as their likely impact on implementation and cost-effectiveness. Design issues are briefly presented as background to each option; however, the manual is not intended to replace the services of a qualified engineer in designing site-specific systems.